Plasma light up suppression

ABSTRACT

A method for suppressing arcing in helium distribution channels of an electrostatic chuck in a plasma processing chamber, wherein the electrostatic chuck is connected to a voltage source for providing a chucking voltage and wherein the plasma processing chamber comprises a process gas source, and a plasma power source for transforming the process gas into a plasma is provided. A gas is flowed through the helium distribution channels of an electrostatic chuck to a back side of a wafer. The gas comprises helium and an electronegative gas.

BACKGROUND

The disclosure relates to a method and apparatus for formingsemiconductor devices on a semiconductor wafer. More specifically, thedisclosure relates to light up suppression in a substrate support duringthe formation of semiconductor devices.

Semiconductor processing systems are used to process substrates such assemiconductor wafers. Example processes that may be performed on suchsystems include, but not limited to, conductor etch, dielectric etch,atomic layer deposition, chemical vapor deposition, and/or other etch,deposition or cleaning processes. A substrate may be arranged on asubstrate support, for example, a pedestal, an electrostatic chuck(ESC), in a processing chamber of the semiconductor processing system. Asubstrate support may include a ceramic layer with embedded heaters,high voltage electrodes and also a base plate bonded to the ceramiclayer. A substrate support may further include helium distributionchannels for supplying helium to the backside of a wafer to control thethermal conductivity between a substrate and a substrate support.Semiconductor processing systems may implement plasma processes (e.g.,plasma etch processes) that require high RF power which will cause highvoltages to appear at a substrate support. The increase in voltageapplied across the substrate support may cause undesired effects such asarcing or gas light up in helium distribution channels and/or othercavities of the substrate support. Light up may damage the semiconductordevices and the processing chamber, create particle defects on thewafer, damage semi-conductor devices on a wafer, etc., thus increasingcosts and equipment down time and decreasing product yield.

SUMMARY

To achieve the foregoing and in accordance with the purpose of thepresent disclosure, a method for suppressing arcing in heliumdistribution channels of an electrostatic chuck in a plasma processingchamber, wherein the electrostatic chuck is connected to a voltagesource for providing a chucking voltage and wherein the plasmaprocessing chamber comprises a process gas source, and a plasma powersource for transforming the process gas into a plasma is provided. A gasis flowed through the helium distribution channels of an electrostaticchuck to a back side of a wafer. The gas comprises helium and anelectronegative gas.

In another manifestation, an apparatus for plasma processing a wafer isprovided. An electrostatic chuck is provided for supporting a wafer,wherein the electrostatic chuck has helium distribution channels forproviding a cooling gas to a backside of the wafer. A helium andelectronegative gas source is in fluid connection with the heliumdistribution channels.

These and other features of the present invention will be described inmore details below in the detailed description of the invention and inconjunction with the following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is a high level flow chart of an embodiment.

FIG. 2 is a schematic view of a plasma processing chamber that may beused in an embodiment.

FIG. 3 is a schematic view of a computer system that may be used inpracticing an embodiment.

FIG. 4 is an enlarged schematic view of an ESC gas source in anotherembodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference toa few preferred embodiments thereof as illustrated in the accompanyingdrawings. In the following description, numerous specific details areset forth in order to provide a thorough understanding of the presentinvention. It will be apparent, however, to one skilled in the art, thatthe present invention may be practiced without some or all of thesespecific details. In other instances, well known process steps and/orstructures have not been described in detail in order to notunnecessarily obscure the present invention.

FIG. 1 is a high level flow chart of an embodiment. In this embodiment,a substrate is placed in a processing chamber on an electrostatic chuck(step 104). A light up suppression gas is flowed through theelectrostatic chuck to cool a backside of the substrate (step 108). Achucking voltage is applied (112). The substrate is processed (step116).

Example

In a preferred embodiment of the invention, a substrate is placed in aprocessing chamber on an electrostatic chuck (step 104). FIG. 2 is aschematic view of a plasma processing chamber that may be used in anembodiment. In one or more embodiments, the plasma processing system 200comprises a gas distribution plate 206 providing a gas inlet and anelectrostatic chuck (ESC) 208, within a processing chamber 249, enclosedby a chamber wall 250. Within the processing chamber 249, a substrate212 is positioned on top of the ESC 208. The ESC 208 may provide achucking voltage from the ESC source 248. A process gas source 210 isconnected to the processing chamber 249 through the distribution plate206. An ESC gas source 251 provides an ESC gas through an inlet 213 tohelium distribution channels 214. The helium distribution channels arein fluid connection with coolant ports 216 to provide coolant to thebackside of the substrate 212 to control the thermal conductivitybetween the substrate 212 and the ESC 208. An RF source 230 provides RFpower to a lower electrode 234. In this embodiment, an upper electrodeis the gas distribution plate 206. In a preferred embodiment, 400 kHz, 2MHz, 60 MHz, and 27 MHz power sources make up the RF source 230. In thisembodiment, one generator is provided for each frequency. In otherembodiments, the generators may be in separate RF sources, or separateRF generators may be connected to different electrodes. For example, theupper electrode may have inner and outer electrodes connected todifferent RF sources. Other arrangements of RF sources and electrodesmay be used in other embodiments, such as in another embodiment theupper electrodes may be grounded. A controller 235 is controllablyconnected to the RF source 230, the ESC source 248, an exhaust pump 220,the ESC gas source 251, and the process gas source 210. An example ofsuch a plasma processing chamber is the Exelan Flex™ etch systemmanufactured by Lam Research Corporation of Fremont, Calif. The processchamber can be a CCP (capacitive coupled plasma) reactor or an ICP(inductive coupled plasma) reactor.

FIG. 3 is a high level block diagram showing a computer system 300,which is suitable for implementing a controller 235 used in embodimentsof the present invention. The computer system may have many physicalforms ranging from an integrated circuit, a printed circuit board, and asmall handheld device, up to a huge super computer. The computer system300 includes one or more processors 302, and further can include anelectronic display device 304 (for displaying graphics, text, and otherdata), a main memory 306 (e.g., random access memory (RAM)), storagedevice 308 (e.g., hard disk drive), removable storage device 310 (e.g.,optical disk drive), user interface devices 312 (e.g., keyboards, touchscreens, keypads, mice or other pointing devices, etc.), and acommunication interface 314 (e.g., wireless network interface). Thecommunication(s) interface 314 allows software and data to betransferred between the computer system 300 and external devices via alink. The system may also include a communications infrastructure 316(e.g., a communications bus, cross-over bar, or network) to which theaforementioned devices/modules are connected.

Information transferred via communications interface 314 may be in theform of signals such as electronic, electromagnetic, optical, or othersignals capable of being received by communications interface 314, via acommunication link that carries signals and may be implemented usingwire or cable, fiber optics, a phone line, a cellular phone link, aradio frequency link, and/or other communication channels. With such acommunications interface, it is contemplated that the one or moreprocessors 302 might receive information from a network, or might outputinformation to the network in the course of performing theabove-described method steps. Furthermore, method embodiments of thepresent invention may execute solely upon the processors or may executeover a network such as the Internet, in conjunction with remoteprocessors that share a portion of the processing.

The term “non-transient computer readable medium” is used generally torefer to media such as main memory, secondary memory, removable storage,and storage devices, such as hard disks, flash memory, disk drivememory, CD-ROM, and other forms of persistent memory, and shall not beconstrued to cover transitory subject matter, such as carrier waves orsignals. Examples of computer code include machine code, such as oneproduced by a compiler, and files containing higher level code that areexecuted by a computer using an interpreter. Computer readable media mayalso be computer code transmitted by a computer data signal embodied ina carrier wave and representing a sequence of instructions that areexecutable by a processor.

In this example, a light up suppression gas consisting essentially ofhelium and oxygen is flowed from the ESC gas source 251 to the heliumdistribution channels in an ESC 214 (step 108). In this example, thelight up suppression gas is 1% to 30% oxygen, with the remaining gasbeing helium. In an example, the light up suppression gas is flowedthrough the helium distribution channels 214 at a pressure of 10 to 80torr.

A chucking voltage is applied (step 112). In this example, chuckingvoltage of −2000 to −2900 volts is provided.

The substrate is processed (step 116). In this example, the process is adielectric etch process. In this example, a process gas comprising 18sccm C₄F₈, 19 sccm O₂, and 400 sccm Ar is flowed from the process gassource 210 into the processing chamber 249, while a chamber pressure of70 to 90 mTorr is maintained. RF power is provided to form the processgas into a plasma. In this example, 3000 Watts is provided at 2 MHz,1500 Watts is provided at 27 MHz, and 500 Watts is provided at 60 MHz.High chucking voltages are used as plasma self biasing voltagesincrease. In this example, the light up suppression gas prevented lightup. No arcing traces were observed at a backside of a wafer that wasprocessed.

To test the effectiveness of the addition of oxygen, the same processwas performed using pure He instead of the light up suppression gas. Insuch a test, light up occurred. This shows that the addition of oxygento the helium distribution gas made a difference to suppress oreliminate light up.

It would not be obvious to add oxygen to helium, since oxygen had beenviewed as being detrimental when added with helium, because oxygenreduces thermal contact between ESC and wafer, and would leak into theprocess chamber, which might change the process. In various experimentsit was found that the addition of oxygen did not cause any loss ofclamping and temperature distribution compared to using pure helium.Clamping is needed to hold the substrate to the electrostatic chuck.Since thermal diffusivity is proportional to the inverse of the squareroot of the molecular mass, a gas consisting essentially of oxygen andhelium has less thermal diffusivity than helium alone. Variousexperiments have found that the addition of oxygen did not impactthermal diffusivity enough to affect temperature of the wafer. Inaddition, some oxygen may leak into the processing chamber. It was foundthat the small amount of oxygen leakage was not significantlydetrimental to the process.

Processing substrates using extreme electrical voltage values has, inthe prior art, caused arcing in the helium distribution channels. Sucharcing damages both the substrate and the processing chamber. Thisresults in device defects in addition to lost time repairing the damagedprocessing chamber. Various apparatus and methods have been used toreduce arcing. However, such apparatus and methods are not completelyeffective or may interfere with the process. In addition, such devicesare complex and expensive.

Without being bound by theory, it is believed that since oxygen is anelectronegative gas, the addition of oxygen suppresses discharge bycapturing free electrons, thus inhibiting discharge. Free electrons inthe gas are necessary to ignite plasma; if these electrons are removed,no arcing can occur. Electronegative gases (such as oxygen, fluorine,chlorine, etc.) are believed to capture free electrons, making themattached to an atom. Once bound the formerly free electrons cannotcontribute into the arcing event. Hence, the introduction of anelectronegative gas into the flow of the main cooling gas reduces thenumber of free electrons below threshold levels necessary to sustain aplasma discharge. In other embodiments, other electronegative gases suchas fluorine, chlorine, and SiH₄ may be used. However, oxygen ispreferred since oxygen is less hazardous and less chemically reactive.In the specification and claims, a gas that is electronegative has anelectronegativity on a Pauline scale of at least 3.00.

Various embodiments reduce or eliminate damage due to light up (arcingin the helium distribution channels), which reduces damage to the waferand device defects. It also increases productivity and provides for agreater safe operational parameter space. Providing greater safeoperational parameters allows for a wider range of processes that may beperformed by the process chamber. The lifetime of the processing chamberis also extended.

In one embodiment, the ESC gas source may be a single source of bothoxygen and helium, such as a container with a mixture of helium andoxygen, where oxygen is 1% to 30% of the total gas measured by a ratioof moles of oxygen divided by the total number of moles. FIG. 4 is anenlarged schematic view of an ESC gas source in another embodiment. Inthis embodiment, the ESC gas source 251 comprises an oxygen source 404and a helium source 408. The oxygen source 404 is connected to an oxygenvalve 412. The helium source 408 is connected to a helium valve 416. Theoxygen valve 412 and helium valve 416 are connected to the inlet 213. Inthis example since there is a separate oxygen source 404 and heliumsource 408 the oxygen valve 412 and the helium valve 416 may be used toprovide the desired helium to oxygen flow ratio.

Preferably, an RF average power of more than 3,000 Watts is provided. Insome embodiments, the RF power is provided at 7,000 to 40,000 Watts.More preferably, the RF power is provided at 5,000 to 20,000 Watts. Invarious embodiments, the chucking voltage has a magnitude of at least500 volts. More preferably, the chucking voltage has a magnitude of atleast 2000 volts. More preferably, various embodiments have a chuckingvoltage between −2000 volts to −3000 volts.

Other embodiments may be used in an inductively coupled process chamber.Other embodiments may use an electrostatic chuck with inner and outerheating zones. To provide inner and outer zones, seal bands may beraised ridges that isolate inner and outer zones. In addition, mesas maybe placed between the seal bands and may provide additional support.

While this invention has been described in terms of several preferredembodiments, there are alterations, modifications, permutations, andvarious substitute equivalents, which fall within the scope of thisinvention. It should also be noted that there are many alternative waysof implementing the methods and apparatuses of the present invention. Itis therefore intended that the following appended claims be interpretedas including all such alterations, modifications, permutations, andvarious substitute equivalents as fall within the true spirit and scopeof the present invention.

What is claimed is:
 1. A method for suppressing arcing in heliumdistribution channels of an electrostatic chuck in a plasma processingchamber, wherein the electrostatic chuck is connected to a voltagesource for providing a chucking voltage and wherein the plasmaprocessing chamber comprises a process gas source, and a plasma powersource for transforming the process gas into a plasma, comprising:flowing a gas through the helium distribution channels of theelectrostatic chuck to a back side of a wafer, wherein the gascomprises: helium to cool the back side of the wafer; and anelectronegative gas for suppressing arcing in helium distributionchannels of the electrostatic chuck in the plasma processing chamber. 2.The method, as recited in claim 1, wherein the electronegative gascomprises at least one of O₂, F₂, Cl₂, or SiH₄.
 3. The method, asrecited in claim 2, further comprising: applying a chucking voltage fromthe voltage source; flowing a process gas from the process gas source toa front side of the wafer; and forming the process gas into a plasma. 4.The method, as recited in claim 3, wherein the chucking voltage has amagnitude of at least 500 volts.
 5. The method, as recited in claim 4,wherein the forming the process gas into a plasma comprises providingmore than 3,000 watts RF average power from the plasma power source tothe process gas.
 6. The method, as recited in claim 5, wherein thecooling gas consists essentially of He and O₂.
 7. The method, as recitedin claim 1, further comprising: applying a chucking voltage from thevoltage source; flowing a process gas from the process gas source to afront side of the wafer; and forming the process gas into a plasma. 8.The method, as recited in claim 7, wherein the forming the process gasinto a plasma comprises providing more than 3,000 watts RF average powerfrom the plasma power source to the process gas.
 9. The method, asrecited in claim 1, wherein the chucking voltage has a magnitude of atleast 500 volts.
 10. The method, as recited in claim 1, wherein thecooling gas consists essentially of He and O₂.
 11. The method, asrecited in claim 1, wherein the electronegative gas comprises oxygen,wherein the oxygen is 1% to 30% of the gas measured by a ratio of moles.